A conventional screw compressor as shown in FIGS. 6,7 comprises: a housing H, two intermeshing rotors R, R' respectively secured on two shafts S, S' rotatably mounted in the housing H for sucking air or gas from the inlet suction port I and compressing the air or gas to be discharged through the outlet port E. The rotor R has an equal depth D for the groove G between adjacent teeth T and a rotor chamber C for mounting the rotors R, R' therein having an equal diameter of the rotor chamber and an equal diameter of each rotor tooth T.
However, such a conventional compressor has the following drawbacks:
1. The grooves G of constant depth D among the teeth T to the length of the rotor R are provided for delivering the intake air or gas only, while the compression is essentially done adjacent the outlet port E to cause a great friction or compression heat produced near the outlet port E; the heat thus accumulated may deteriorate the machine parts or materials, consuming shaft work and decreasing the compression efficiency.
2. For ensuring a complete stroke for delivering the air or gas to be compressed through the grooves in the rotors, the length of the rotor and shaft can not be shortened, thereby occupying a big space for accommodating such a compressor.
3. A sudden compression occurring adjacent the outlet port E may cause serious molecular collision of the fluid and vibration of the equipment, easily causing noise pollution.
4. The long rotor and shaft may decrease the rigidity, being easily vibrated or damaged.
5. For overcoming any excessive gas backflow through such a long rotor, a higher rotor tangential speed should be maintained to easily cause noise and also waste much shaft work.
The present inventor has found the drawbacks of the conventional screw compressor, and invented the present screw compression equipment with gradationally contracted rotor diameter and spiral grooves.